Solar inverters are used for converting the direct current delivered by solar panels into an alternating current for feeding into a public power network or into a stand-alone power network. In such cases solar inverters generally feature measurement circuits by means of which the operating status can be detected and recorded as well as featuring various configuration options. A request for measurement data (e.g. curve of the input voltage, converted energy etc.) and changes to settings (e.g. standby times) can be undertaken ether through a direct connection of a solar inverter to an input/readout device or by means of a connection to a communication network. In the latter case the input/readout device forms a node of the communication network and the data is transmitted via its physical structure. The World Wide Web is typically used as the communication network, but an Intranet or an Extranet can also be used.
According to the prior art a photovoltaic system either has a central communication facility to which all solar inverters of the installation are connected or each solar inverter includes a separate communication unit which allows a direct connection to a communication network.
Thus DE 198 59 732 A1 for example describes a photovoltaic system with a plurality of solar modules and a control center, with each solar module being assigned an inverter and each inverter being connected via an ac power line to the control center. Both data and also the energy generated by the solar modules are transmitted using a time division multiplexing method. In such cases the individual inverters can only be connected via the control center to the public power network; therefore the installation as a whole only functions if the control center is operating correctly. Data transmission in this case is only used for diagnosis of the operating state of the solar modules along with the respective inverters. Control commands (e.g. switch on/switch off) are only possible for the installation as a whole by changing the settings at the control center, there is no provision for being able to control individual solar inverters.
US 2004/0027004 A1 discloses a general communication structure for decentralized power generation units. In this case either each power generation unit or each of a number of groups of power generation units has a microcontroller, with all microcontrollers being connected to a communication network. For connection to the communication network each microcontroller has a communication unit (e.g. modem), via which communication processes are handled. Such a communication structure requires each microcontroller to be connected via at least a telephone line or a network cable to the communication network. These lines are mostly very thin and have many strands, which means that great care must be taken when laying them to avoid damaging the cable. This type of cabling of inverters for solar modules which naturally has be installed scattered in the countryside and on buildings and is often not freely accessible, is therefore associated with a certain outlay. With an Ethernet connection the length of the lines is also restricted without the corresponding repeaters.